NFL Comeback Analysis

How important is momentum to comeback and win a game? Often when a team is down big in the first half we hear announcers say how important a score at the end of the half can be towards shifting momentum and winning the game; but is that really the case?

Does scoring at the end of the first half help a team win the game? I looked into it.

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I analyzed regular and postseason NFL play-by-play data since 2009. Games were only looked at if a team was trailing by 17 or more points heading into the half. I picked this number because it makes it a three score game, which is quite the obstacle to overcome.

Since 2009 there have been 486 games with a 17 or more point score differential going into halftime. Of these, only 31 teams have comeback to win – that’s 6.38%.

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First, I looked at a team’s passing stats, average expected points added (EPA), in both halves. The below graphic is only for teams who comeback to win.

It’s clear, and pretty logical, that teams who overcome this 17 point deficit play better in the second half. We see above that all but one team had a better second half EPA per pass than the first (the one exception being the Jacksonville Jaguars on 11/30/2014).

Teams had an average passing EPA of about -.3 in the first half, but had a second half average passing EPA of about .5 – that’s almost an entire point difference between halves.

But what about the teams who don’t overcome the deficit? I plotted those below.

Both first and second half average passing EPA is lower than when teams win. Notable too, is that the average for both halves is below 0, which makes sense – a team that is down by 17 points at half is clearly not playing well.

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What about the running game? I didn’t know what to think of this because the prevailing logic to overcome a 17 point deficit would be to pass – a team needs to score a lot and score quickly.

Like before, I plotted the average rushing EPA per half for every team that won and lost with a 17 point deficit at half.

Teams are certainly more scattered here than with passing, but the same general trend holds: teams that comeback to win ran the ball better in the second half.

The average first half rushing EPA is about -.25 and the average second half rushing EPA is about .15. While still an improvement, it is nothing compared to the increase we see with average passing EPA between halves.

And, what about the rushing stats for teams that lost?

Same story. Bad first and second half running stats, both of which have negative average EPA

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Clearly playing better in the second half is needed if a team wants to overcome a deficit at half to win, but do they need to score at the end of the first half to win?

Of the teams that have overcome this deficit only 10 scored in the last 5 minutes of the half, just 32.25%. Clearly this is not a silver bullet. However, 20 teams that comeback to win have scored within the first 5 minutes of the second half.

Overall, 23 teams, or 74.19%, score in the last 5 minutes of the first half, or the first 5 of the second half – clearly scoring at the end OR beginning is important.

Now, for the the teams that lost. 82 (18.02%) score at the end of the first half, 150 (32.96%) score at the start of the second , and only 199 (43.73%) of teams score in the last 5 minutes of the first half, or the first 5 of the second half – much lower than the winning teams.

So is scoring at the end of the half important? Yes.

Does it guarantee victory? No.

It’s clear that scoring does help a team win, but above we showed how important it is to just play a better second half. Can scoring at the end of the half help that? Maybe. Perhaps there is something to be said about scoring at the end, then having halftime to reset, but someone who is much more statistically skilled than me will have to look into that.

Data: nflfastR